A delayed coker is a unit that thermally converts vacuum distillation column bottoms residue product into lighter distillate and coke. The coking process is primarily a semi-batch process with two or more coke drums operating in pairs in alternating cycles—one drum is filled while the other is emptied. Typically, one coke drum is filled with a batch of heated feed material, such as vacuum distillation column bottoms residue product (also known as “vacuum resid”), that has been heated to a high temperature, between about 830 to 950 degrees Fahrenheit (“° F.”), at a low pressure, between about 15 to 60 pounds per square inch gauge (“psig”). The batch of feed material is allowed to thermally react in the coke drum for a period of time. The gaseous reaction products of the thermal cracking are removed from the top of the coke drum and sent to a fractionator. The remaining reaction products remain in the drum and solidify into a product known as petroleum coke, or simply coke. The coke drum is then steamed, cooled and vented, after which the coke drum is opened to the atmosphere and the coke is removed from the drum by cutting it up with high pressure water into small chunks and allowing it to drop out of a large opening at the bottom of the drum. Typically, a single batch of coke may be formed during one cycle that allows the coke drum to be filled for a coking period of between 12 to 18 hours. Thus, one complete fill, coke and unload cycle typically will be double this time.
Originally, this process was operated manually. Human operators would open and close valves manually in a predetermined sequence to route the feed to one coke drum, while other valves are opened and closed to isolate the other drum that is full of coke product ready to be emptied. The delayed coker unit may include up to twenty or more sets of valves for each coke drum, with some valve sets including two valves for a double-block isolation. As such, it can be a very labor intensive operation to open and close the valves in a precise sequence required for safe operation of the delayed coker during each coke drum cycle with very short times of at most a few hours between each step requiring numerous valve position changes. Because some valves in the unit are on process lines that are exposed to both hydrocarbons and the atmosphere at different parts of the cycle, it is important to avoid exposure of hot hydrocarbon to oxygen by verifying the right valves are closed and/or open at each step of the process.
Beginning in the 1990's, delayed coker process units began to take advantage of automation equipment. Manually operated isolation valves were replaced with locally operated motor operated valves and then remotely controlled motor operated valves. Additional double block valves for ensured isolation were installed in some locations. Remotely operated automated top and bottom deheading valves replaced manually operated deheading valves. Electronic safety interlock systems were added to verify valve position and prevent operators from opening the wrong valves or correct valves at the wrong time that might expose heated hydrocarbons to the atmosphere, or expose the operators to the hot hydrocarbons. Partial automation of portions of a delayer coker operation have been proposed. Despite these improvements, the operation of a delayed coker still requires significant labor of human operators in the unit.